Antibiotic for Treatment of IBS

Based on theory that there might be overgrowth of bacteria in the small bowel (SBO) in patients with IBS antibiotics have been tried as a treatment. Antibiotics have helped some suffering with IBS, especially, those with complaints of diarrhea, excess bloating and gas, and abdominal pain.

Without well-designed scientific studies showing clear cut effectiveness, the use of antibiotics has been somewhat empiric and the questions have continued to be which antibiotic, for how long and how often? Furthermore, the role of SBO has been over stated in past, with an estimate of only 5-10% of IBS patients having confirmed bacterial overgrowth. However, more recently the role of post-infectious IBS and altered gut flora in IBS as well as the availability of non-absorbed antibiotics like Rifaximin and high quality probiotics such as VSL#3 has led to increased interest in antibiotic and probiotic therapy.

Two recent multicenter randomized, double-blind, placebo-controlled trials, TARGET 1 and TARGET 2, involving over a thousand patients who were given either Rifaximin or placebo have shown favorable though not "earth shattering" results. The dose of Rifaximin was 550 mg 2-3 times a day versus placebo, for two weeks followed by another 10 weeks of follow-up. Constipated IBS patients were excluded. Bloating and a global assessment of IBS symptoms by a standardized scale were the primary endpoints whereas abdominal pain and stool frequency were secondary endpoints.

Abdominal pain, bloating and stool symptoms were all better following treatment with Rifaximin. When data from both studies were combined it was noted that 41% of those receiving Rifaximin versus 32% in placebo group (30% placebo response rate typical in most treatment studies). Though this achieved statistical significance, it isn't a great response rate, significantly less than 50% noting response. There was a statistically significant improvement noted over the three month study period.

Limitations to the study from my stand are that markers for leaky gut and IBD serology were not checked nor were stains for mast cells done on these patients. Patients did not receive probiotics either.

One major advantage of Rifaximin is that is not absorbed from the GI tract so there are no systemic side effects. It also tends to quickly if it works and has been documented to last up to three months. The disadvantage is that it is expensive, often not covered by insurance and doesn't work in more than half of those trying it. Addition of a probiotic may help though there are limited studies to support this as a formal recommendation. A theoretical disadvantage is possible selecting out more resistant bacteria in the gut.

It is a regimen that may be worth a try if your insurance covers the antibiotic. I would recommend that Celiac disease, inflammatory bowel disease (ulcerative colitis and Crohn's disease), and microscopic colitides (lymphocytic colitis, collagenous colitis and mastocytic enterocolitis) be excluded by blood tests and endoscopies with biopsies.